How much accurate are the PS movements measured?
The precision of surveys accomplished by the PS Technique depends on the number of images available over the area of interest, on the stability of each PS and on the distance of the PS from the reference point. This point is a point of known elevation and supposed to be motionless. Precision of displacement measurements is always between 0.1 and 0.5 millimetres per year in case of average velocities. At a distance of less than 4 ~ 5 km from the GCP, accuracy of velocity can be 0.1 millimetres per year. In case of single measurements, displacement accuracy is around 1 ~ 3 mm. The average displacement velocity of each PS is provided to the customers together with a quality index (called coherence of the PS). The higher the coherence value, the higher the reliability of the displacement measure.
